Art of vulcanizing caoutchouc



CLAYTON W. BEDFORD, OF AKRON, OHIO, ASSIGNOR TO THE GOODYEAR TIRE RUBBERCOMPANY, OF AKRON, 01-110, A CORPORATION OF OHIO.

ART OF VULCANIZING CAOU'ICHOUC.

Specification of Letters Patent.

Patented Mined, 1922.

No Drawing. Original application filed May 17, 1919, Serial No. 297,920.Divided and this application filed November 24, 1919. Serial No.340,262.

To all whom it may concern:

Beit known that I, CLAYTON W. BEDFORD, a citizen of the United States,residing at Akron, in the county of Summit and State of Ohio, haveinvented a new and useful Improvement in the Art of VulcanizingCaoutchouc, of which the following is a all of the sulphur of the rubbermix prior.

to incorporation into said mix to be vulcanized. In accordance therewithit is possible to carry out the reaction between the nitrogenaccelerator and the sulphur at the temperature best suited thereto, toremove undesired gaseous or other by-products formed as the result ofsaid reaction and in many cases to employ nitrogen acceleracterized asSchilfs bases, which may be defined in general terms as theanhydro-reaction products of aldehydes and primary amines. As a limitingexample of such compounds I intend also to includehexamethylenetetramine, which may be regarded as an anhydro-condensationproduct of formaldehyde and ammonia. It has furthermore been found thatthose of the said bases containing the methylene group are productive ofparticularly advantageous results in the process of the presentinvention.

As will be more fully hereinafter set forth, in the initial stage of theprocess wherein the nitrogen accelerator is reacted upon directly bysulphur, all of the sulphur.

as well as the course of the reaction.

An illustration of the process of the present' invention, themethylene-containing Schiffs base, methylenediphenyldiamine (C II NH),.CH may be caused to react with sulphur in the following proportions byweight:

198 parts methylene-diphenyldiamine,

64 parts sulphur.

These ingredientsare slowly melted and then heated to 120150 C. untilapproximately 34 parts by weight of gas (corresponding to approximately1 mol of. H 8) arev eliminated. The reaction product is then steamdistilled, about 93 parts (1 mol) of aniline which has been producedduring the reaction being thereby removed.

The product is a somewhat brittle reddish brown to yellowish brownamorphous mass having a conchoidal fracture and with a softening pointso low that it may be compounded in the rubber mix without grinding.

In forming a rubber mix with the sulphur nitrogen accelerator thusproduced, whereby the curing powers thereof may be illus-' trated, 16parts of zinc oxide, 16 parts of plantation pale-crepe rubber, one partof sulphur and 0.90, parts of the sulphur nitrogen accelerator abovedescribed may be mixed by the ordinary methods in rubber compounding.Such a mix will vulcanize in from fifteen to twentyminutes, whereas witha nitrogen accelerator not previously treated with sulfur and used inlarger amounts (from 1.00 to 1.25 parts in the same mix) a curing periodof approximately forty five minutes is required. Furthermore the rubberproduced by the use of the methylene-diphenyldiamine-sulphur acceleratoris of somewhat higher tensile strength and- This product and sulphur maybe caused to react in the following proportions:

210 parts (1 molecule of di-polymer) methylene-anil1ne,

64 parts sulphur.

These ingredients are slowly melted together and then heated to 150 to170 C. until 34 to 36 parts of gas are removed. This gas consistsprincipally of H 55. Some CS is also produced and eliminated in thecourse of the reaction. The product is then distilled until no moreaniline passes over, the entire amount of aniline produced -dur ingreaction being thus driven off. After removal of the aniline the productis an amorphous dark reddish brown solid having resinous properties. Itis brittle and may be ground; its softening point is, however,sufiicicntly low that grinding is not necessary for rubber compounding.The sulphur nitrogen accelerator thus produced may be incorporated intoa mix of substantially the character of that previously described,likewise decreasing the length of time of cure and improving the tensileand elastic qualities of the vulcanized product.

As a further illustration of the reaction of such bases with sulphur,hexamethylenetetramine and sulphur may be caused to react in proportions(1 mol of hexamethylenetetramine to at least 4 mols of sulphur). Thisreaction results in an evolution of gas, and in 1 the formation ofyellow vapors which may b condensed as a reddish oil and a residualsolid, yellowish brown in color and somewhat soft and'sticky. The solidresidue may be substituted in the example of the rubber mix previouslygiven for the sulphur reaction product named.

As has been previously stated, the reaction between'the nitrogencompounds and the sulphur may take place in the presence of a solventdiluent,.which may in some instances take part in the reaction. Such asolvent or diluent may-be utilized to control the rate and temperatureof the reaction or may likewise be used to modify its course. Thearomatic amines, and particularly aniline, has been found to beparticularly use ful and advantageous in forming the sulphur-nitrogenaccelerators in the initial stage of the vulcanizationprocess.

As an illustration of the use of a solvent diluent and particularlyaniline, I may utilize methylene-aniline, sulphur and aniline in thefollowing proportions:

210 parts methylene-aniline 128, parts sulphur 372 parts aniline Themethylene-aniline and aniline are boiled under a reflux condenser forfive hours at a temperature of 195 to 198 C.

(thermometer in the liquid). The mixture isithen cooled to 150 C., atwhich point the sulphur is added. The temperature is now'raised slowlyto 175 C. and held until 56 to 60 parts by weight of gas, principallyhydrogen sulphide are lost. .The free aniline is now distilled off,preferably by steam distillation, care being taken to re move the lastof the aniline from the reaction mixture to such an extent that theproduct will cool to a hard, brittle mass.

On using 1.25 parts of the sulphur-nitrogen accelerator thus produced ina rubber mix containing 1 part of sulphur, 16 parts zinc oxide and 16partsof plantation palecrpe rubber, th mix will cure in approximatelyfifteen to twenty minutes, whereas if the nitrogen acceleratormethylene-aniline is used inthe same mix, even to the extent of 1.5parts, the time of cure is forty five to fifty minutes. In addition toshortening the time of cure, thereby increasing the output of a givenequipment, the product wherein the sulphur-nitrogen accelerator in usehas a higher tensile strength, a higher modulus ofelasticity and itsquality is otherwise improved.

Methylene diphenyldiamine may likewise be utilized in a reaction similarto the above, substituting for the methylene-aniline a molecular.proportion of the methylene diphenyldiamine. Hexamethylenetetramine mayalso be substituted in the reaction with sulphur and aniline, as abovedescribed, the product resulting from its use having the characteristicsof a mixture of the product resulting from the use ofmethyleneanilin andmethylene diphenyldiamine' in the presence of aniline together with,apparently, the product of reaction of hexamethylene with sulphuix' Theproduct of reaction of methylene diphenyldiamine or ofhexamethylenetetramine with sulphur in in the rubber mix for the sulphurnitrogen accelerator in the example previously given.

The initial reaction between the nitrogen compounds and the sulphur maybe effected either in the presence or in the absence of aniline or othersolvent diluents, as is indicated by the above examples andillustrations given. Other solvent diluents than aniline may be used,for example, xylol, for the purpose of controlling the rate andtemperature of reaction, but in general I prefer that a compound of thearomatic amine class, such as aniline, paratoluidine, or the like, beused.

This application is a division of my application Serial No. 297,920,filed May 17,

.. ing together under reacting conditions sulphur and a methylenegroup-containing Schiff base.

2. The process of producing a sulphurnitrogen accelerator which consistsin bringing together under reacting conditions sulphur and methylenediphenyldiamine.

3. The process of producing a sulphurnitrogen accelerator which consistsin bringing together methylenediphenyldiamine with sulphur, heating themixture, and removing the gases andaniline formed.

4. The process of producing a sulphur nitrogen accelerator, whichconsists in bringing together under reacting conditions sulphur and amethylene group-containing Schiflf base in the presence ,of a solventdiluent.

5. The process of producing a sulphurnitrogen accelerator which consistsin bringing together under reacting conditions sulphur and a methylenegroup-containing Schiff base in the presence of an aromatic amine.

6. The process of producing a sulphurnitrogen accelerator which consistsin bringing together under reacting conditions sulphur and methylenediphenyldiamine in the presence of aniline.

7. As an accelerator in the vulcanization of rubber the resinous massproduced by the reaction of sulphur on methylene diphenyldiamine.

CLAYTON W. BEDFORD.

